ANS:A - at < 100

Steam distillation is a process used to distill volatile compounds that are not easily distilled by conventional methods. It involves the use of steam to carry the volatile compounds with it as it rises through the distillation apparatus. In the case of nitrobenzene (with a boiling point of 210.6°C) being steam distilled at 1 atm pressure, the temperature at which nitrobenzene will distill off will indeed be below 100°C. During steam distillation, the presence of steam allows compounds with higher boiling points to vaporize at lower temperatures than their normal boiling points. The steam effectively carries the nitrobenzene with it, allowing it to distill off at a temperature lower than its boiling point under normal conditions. So, the correct answer is: at < 100°C.